Biomedical Engineering Reference
In-Depth Information
Fig. 3.8 The local structure of the 6-Se-G modification. The Se-G3/C5 base pair (2R7Y) with the
experimental electron density shows three hydrogen bonds (exo-6-Se/exo-4-NH2, 1-NH/N3, and
exo-2-NH2/exo-2-O) with bond lengths in 3.48, 3.16, and 2.59 A, respectively
makes DNA yellow color. This unique property offers great potentials to create
colored DNA nanostructure and devices and allow nucleic acid direct diagnosis and
visualization [ 86 ].
3.4.3
Other Selenium Modifications on Nucleobases
After site-specifically replacing carbonyl oxygen with selenium or sulfur, the
nucleosides show several unique properties, including altered base-pairing fidelity,
unique UV or fluorescent property, as well as anomalous signal for crystallographic
purpose. The selenium moiety has also been introduced to the 5-position of pyrimi-
dine nucleosides for structure-and-function study, including 5-methylseleno-T [ 21 ]
and 5-methylseleno-C [ 87 ]. It is worth mentioning that both of these modifications
allow the duplex to maintain the similar overall structure and thermal stability.
Besides their application in elucidating nucleic acid 3D structures by the selenium
MAD and SAD phasing, they also provide potential in related functional studies.
For instance, in 5-methyloxy-T-containing Se-DNAs, the hydrogen on methyloxy
group forms hydrogen bond with 5 0 -phosphate backbones [ 21 ]. The comparison
with the 5-Se-T-DNA helps to confirm this striking observation: the nucleobase
can interact with its phosphate backbone to stabilize the local conformation. This
observation could provide new insights into mechanism of phosphorylation and
dephosphorylation. Interestingly, the 5-methylseleno-C-modified DNAs could be
utilized to investigate the cytidine methylation of genomic DNA.
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